Conventional Chemical Vapor Deposition Research Articles

Hemodynamic parameters and diabetes mellitus in community-dwelling middle-aged adults and elders: a community-based study

Hemodynamic parameters have been correlated with stroke, hypertension, and arterial stenosis. While only a few small studies have examined the link between hemodynamics and diabetes mellitus (DM). This case-control study enrolled 417 DM patients and 3475 non-DM controls from a community-based cohort. Peak systolic velocity (PSV), end-diastolic velocity (EDV), blood flow velocity (MFV), pulsatility index (PI), and the resistance index (RI) of the common carotid arteries were measured by color Doppler ultrasonography. Generalized linear regression analyses showed that as compared to the non-DM controls, the age-sex-adjusted means of PSV, EDV, and MFV were − 3.28 cm/sec, − 1.94 cm/sec, and − 2.38 cm/sec, respectively, lower and the age-sex-adjusted means of RI and PI were 0.013 and 0.0061, respectively, higher for the DM cases (all p-values < 0.0005). As compared to the lowest quartiles, the multivariable-adjusted ORs of DM for the highest quartiles of PSV, EDV, MFV, RI, and PI were 0.59 (95% confidence interval [CI] 0.41–0.83), 0.45 (95% CI 0.31–0.66), 0.53 (95% CI 0.37–0.77), 1.61 (95% CI 1.15–2.25), and 1.58 (95% CI 1.12–2.23), respectively. More importantly, the additions of EDV significantly improved the predictabilities of the regression models on DM. As compared to the model contained conventional CVD risk factors alone, the area under the receiver operating curve (AUROC) increased by 1.00% (95% CI 0.29–1.73%; p = 0.0059) and 0.80% (95% CI 0.15–1.46%; p = 0.017) for models that added EDV in continuous and quartile scales, respectively. Additionally, the additions of PSV and MFV also significantly improved the predictabilities of the regression models (all 0.01 < p-value < 0.05). This study reveals a significant correlation between DM and altered hemodynamic parameters. Understanding this relationship could help identify individuals at higher risk of DM and facilitate targeted preventive strategies to reduce cardiovascular complications in DM patients.

Unique ping-pong daisy-like catalysts: Efficient overall hydrolysis catalysis driven by vanadium-doped Fe2P and Co3(PO4)2 nanosheet composites

Balancing catalytic activity and durability remains a challenge in the development of high performance, inexpensive and durable electrocatalysts. In this study, fully hydrolyzed composite catalyst V–Fe2P@Co3(PO4)2/NF with ping-pong daisy-like morphology was synthesized using conventional hydrothermal and chemical vapor deposition (CVD) processes. In alkaline electrolyte, V–Fe2P@Co3(PO4)2/NF showed excellent electrochemical performance, achieving a current density of 10 mA cm−2 when the driving overpotentials for the hydrogen production reaction (HER) and oxidation reaction (OER) were 56 mV and 178 mV, respectively. Meanwhile, V–Fe2P@Co3(PO4)2/NF demonstrated good durability in terms of both HER and OER stability. Furthermore, the driving voltage required for the electrolyser assembled with V–Fe2P@Co3(PO4)2/NF as the electrode is lower than that of the RuO2/NF||Pt/C/NF electrode, both of which have driving voltages of 1.503 and 1.562 V (10 mA cm−2), respectively. Meanwhile, it achieves a Faraday efficiency of 95%. This study offers a feasible solution towards synthesizing and applying bifunctional water decomposition electrocatalysts.

Graphene synthesis by electromagnetic induction heating: Domain size and morphology control

In this paper we discuss the effect of hydrogen and methane content during low-pressure chemical vapor deposition (LPCVD) of graphene on inductively heated copper foils. By increasing the H2/CH4 ratio by a factor of 5 from 25 to 125, different graphene morphologies ranging from dendritic fractals to compact hexagonal islands are obtained. In addition, increasing the hydrogen concentration allows the nucleation rate to be slowed down by a factor of ∼10 thereby high-quality regular hexagonal graphene single crystals of significant size of 0.1 mm are found. From these measurements, we estimate the activation energy for graphene nucleation in low-pressure CVD (2 eV) and propose a phenomenological law for graphene nucleation. As compared to conventional CVD methods, considerable advantages of inductive heating are outlined, and some fundamental aspects of this approach are discussed.

High-performance blue TADF OLED using two-step heat plasma-treated MoTe2 as a hole-injection layer

In the pursuit to overcome the limitations posed by traditional hole injection layers (HILs), such as PEDOT: PSS, researchers are focusing on innovative strategies to modify electrode/organic interfaces to facilitate charge-carrier injection and reduce the turn-on voltage, particularly in the context of high-efficiency organic light-emitting diodes (OLEDs). Two-dimensional materials show great potential in addressing the energy barrier challenges at electrode/organic interfaces owing to their exceptional optoelectronic properties and robust chemical stability. However, their implementation in OLEDs has been hindered by complex fabrication processes and work function (WF) mismatches. This study presents a novel approach by introducing a magnetron-sputtered MoTe2 as HIL via two-step O2 doping. This strategy enhances the crystallinity of MoTe2 at a relatively low annealing temperature (350 °C), combined with a plasma-treated anode possessing high WF (approximately 5.05 eV), high transmittance (93 % at 478 nm), and low sheet resistance (33 Ω/sq). Consequently, compared with the conventional blue thermally activated delayed-fluorescence OLED using MoO3 as a HIL, the external quantum efficiency of the manufactured device using MoTe2 as a HIL was improved by 57 % and turn-on voltage was reduced to 2.6 V. This study provides a new pathway for overcoming the limitations of conventional solution-based HILs and chemical vapor deposition techniques to industrialize the large-scale manufacturing and commercialization of OLEDs.

Differential pressure sensors based on transfer-free piezoresistive layered PdSe2 thin films

Piezoresistive layered two-dimensional (2D) crystals offer intriguing promise as pressure sensors for microelectromechanical systems (MEMS) due to their remarkable strain-induced conductivity modulation. However, integration of the conventional chemical vapor deposition grown 2D thin films onto a micromachined silicon platform requires a complex transfer process, which degrades their strain-sensing performance. In this study, we present a differential pressure sensor built on a transfer-free piezoresistive PdSe2 polycrystalline film deposited on a SiN x membrane by plasma-enhanced selenization of a metal film at a temperature as low as 200 °C. Based on the resistance change and finite element strain analysis of the film under membrane deflection, we show that a 7.9 nm thick PdSe2 film has a gauge factor (GF) of −43.3, which is ten times larger than that of polycrystalline silicon. The large GF enables the development of a diaphragm pressure sensor with a high sensitivity of 3.9 × 10−4 kPa−1 within the differential pressure range of 0–60 kPa. In addition, the sensor with a Wheatstone bridge circuit achieves a high voltage sensitivity of 1.04 mV·kPa−1, a rapid response time of less than 97 ms, and small output voltage variation of 8.1 mV in the temperature range of 25 °C to 55 °C. This transfer-free and low-temperature grown PdSe2 piezoresistive thin film is promising for MEMS transducer devices.

An investigation into low-temperature HFCVD and derivative techniques for the enhancement of diamond-coated cemented carbide tool performance

The performance of diamond-coated cemented carbide tools manufactured via the conventional hot filament chemical vapor deposition (HFCVD) technique exhibits certain limitations, including issues with poor toughness and reduced adhesive strength of film-substrate systems, primarily attributed to the cobalt diffusion at elevated temperatures (> 800 °C). In this study, a pioneering exploration of a low-temperature diamond film deposition technique on cemented carbide is developed, and a comprehensive evaluation of the film properties is conducted. The results indicate that owing to constraints related to growth rate and diamond film purity, it may not serve as an effective approach for enhancing the performance of conventional coated tools. Nonetheless, the inherent capability of this technique in inhibiting cobalt diffusion is strategically harnessed to pioneer the development of a derivative technique referred to as the “low-temperature to high-temperature HFCVD (LT-HT-HFCVD)”. This innovative method leverages a low-temperature deposited diamond layer as an intermediate layer to impede cobalt diffusion while serving as a densely nucleated layer for subsequent diamond growth. Subsequently, the conventional technique is employed to facilitate an effective growth rate and maintain high growth purity. The diamond-coated tools generated by this technique are subject to a comprehensive comparative analysis against those generated by low-temperature HFCVD (LT-HFCVD) and conventional HFCVD (CT-HFCVD) techniques. The results reveal that tools fabricated using the LT-HT-HFCVD combine the advantages inherent to both the LT-HFCVD and CT-HFCVD techniques, thereby manifesting superior toughness, enhanced film-substrate adhesive strength, and outstanding cutting performance.

Direct growth Bi2O2Se nanosheets on SiO2/Si substrate for high-performance and broadband photodetector

Bi2O2Se, a newly emerging two-dimensional (2D) material, has attracted significant attention as a promising candidate for optoelectronics applications due to its exceptional air stability and high mobility. Generally, mica and SrTiO3 substrates with lattice matching are commonly used for the growth of high-quality 2D Bi2O2Se. Although 2D Bi2O2Se grown on these insulating substrates can be transferred onto Si substrate to ensure compatibility with silicon-based semiconductor processes, this inevitably introduces defects and surface states that significantly compromise the performance of optoelectronic devices. Herein we employ Bi2Se3 as the evaporation source and oxygen reaction to directly grow Bi2O2Se nanosheets on Si substrate through a conventional chemical vapor deposition method. The photodetector based on the Bi2O2Se nanosheets on Si substrate demonstrates outstanding optoelectronics performance with a responsivity of 379 A W−1, detectivity of 2.9 × 1010 Jones, and rapid response time of 0.28 ms, respectively, with 532 nm illumination. Moreover, it also exhibits a broadband photodetection capability across the visible to near-infrared range (532–1300 nm). These results suggest that the promising potential of Bi2O2Se nanosheets for high-performance and broadband photodetector applications.

Vapor–liquid–solid synthesis of Ag2Te using chemical vapor deposition method

Silver telluride, Ag2Te, has been selectively synthesized by conventional chemical vapor deposition (CVD) via the vapor–liquid–solid growth mechanism. The pre-deposited Ag film on the SiO2/Si substrate was chemically reacted with vaporized Te atoms and transformed into liquid-phase Ag–Te during the CVD process. The appropriate supply of Te vapor to the Ag film influenced the stoichiometry of Ag–Te compounds, and the formation of stoichiometric Ag–Te compounds was well-explained by the phase diagram of the Ag–Te system. We found that Ag2Te was grown in the liquid of Ag–Te under the Te-poor condition, while Ag5Te3 and Te were simultaneously solidified under the Te-rich condition. The high-temperature synthesis of Ag2Te showed higher crystallinity and better stoichiometry than the low-temperature synthesis. This study demonstrates that Ag2Te can be selectively synthesized by conventional CVD via delicate control over the phases of the complex Ag–Te system.

(Invited) Growth of Hexagonal Boron Nitride by MOCVD for Electronic and Photonic Applications

Hexagonal boron nitride (h-BN) is a 2-dimensional (2D) layered insulating material. Thanks to its wide bandgap of ~6 eV and high thermal conductivity, h-BN has been widely utilized as an ideal substrate, gate dielectric material, passivation layer, and atomic tunnelling layer for 2D electronic devices. Recently, it has gained more attention as active material for photonics applications due to its potential for stable quantum emitters in the visible spectral range, as well as deep-ultraviolet emitters and detectors due to its exceptionally high internal quantum efficiency despite its indirect bandgap. However, mechanically exfoliated bulk h-BN and h-BN films grown on catalytic metal substrates by conventional chemical vapor deposition (CVD) systems have been mainly used to study the fundamental properties, lacking in scalability for practical implementation of h-BN.Here, we exploit the scalable approach to grow h-BN on various substrates such as sapphire, Si, and GaN, by using metal-organic chemical vapor deposition (MOCVD). A few-layer h-BN films were successfully grown on those substrates. In particular, we successfully accomplished the conformal growth of few-layer h-BN over an array of Si-based nanotrenches with 45 nm pitch and the aspect ratio of ~ 7:1. Moreover, it was found that at a specific MOCVD growth condition, a very unique h-BN film can be grown on GaN substrates, in which few-layer h-BN film is suspended on GaN nanoneedles. The combination of state-of-the-art microscopic and spectroscopic analyses revealed that the suspended h-BN films exhibit unprecedented deep ultraviolet photoluminescence spectra with local variation in band-edge emission. In addition, the h-BN films show unprecedented atomic stacking configuration, the mechanism of which will be discussed with optical and structural characterizations and theoretical calculations.

(Invited) Atomic Layer Deposition as the Enabler for the Meta Stable Semiconductor InN and Its Alloys

Indium nitride (InN) is highly interesting for high-frequency and high-speed electronics given the remarkably high electron mobility in InN. The development of InN based electronics is hampered by the difficulty in depositing high quality thin films. The InN crystal breaks down to indium metal and nitrogen gas at about 500 °C which limits the deposition temperature, making conventional chemical vapor deposition (CVD) poorly suited for InN. Atomic Layer Deposition (ALD) is a low temperature, time-resolved form of CVD where the precursor gases are pulsed sequentially, separated by inert gas. This renders a deposition chemistry fully controlled by surface chemistry. We hypothesized around 2015 that the surface-controlled deposition of ALD will be beneficial for InN deposition and started our activities on ALD of InN.I will describe our work on ALD of InN films where we have focused on ALD process development and design of new precursors. We now can show that ALD is an enabling technology for InN based electronics as it is capable of depositing a few nanometers continuous, epitaxial InN films.[1] I will describe our results on epitaxial growth of InN by ALD using our newly invented In precursor [2] and describe why we believe that the key to the success of ALD for InN is the dynamic gas exchange during the deposition.[3] I will also show our atomic scale understanding of the growth chemistry from quantum chemical modelling,[4] and how the results can be extended to InxGa1-xN.[5, 6]

High-Rate Epitaxial Growth of Silicon Using Electron Beam Evaporation at High Temperatures

This paper describes the high-rate (~1.5 μm/min) growth of Si films on Si supporting substrates with (100) crystallographic orientation at 600 °C, 800 °C, and 1000 °C in a vacuum environment of ~1 × 10−5 mbar using electron beam (e-beam) evaporation. The microstructure, crystallinity, and conductivity of such films were investigated. It was established that fully crystalline (Raman spectroscopy, EBSD) and stress-free epi-Si layers with a thickness of approximately 50 µm can be fabricated at 1000 °C, while at 600 °C and 800 °C, some poly-Si inclusions were observed using Raman spectroscopy. Hall effect measurements showed that epi-Si layers deposited at 1000 °C had resistivity, carrier concentration, and mobility comparable to those obtained for c-Si wafers fabricated through ingot growth and wafering using the same solar grade Si feedstock used for the e-beam depositions. The dislocation densities were determined to be ∼2 × 107 cm−2 and ∼5 × 106 cm−2 at 800 and 1000 °C, respectively, using Secco etch. The results highlight the potential of e-beam evaporation as a promising and cost-effective alternative to conventional CVD for the growth of epi-Si layers and, potentially, epi-Si wafers. Some of the remaining technical challenges of this deposition technology are briefly indicated and discussed.

Sleep duration and Framingham´s cardiovascular risk score: results from the Hoveyzeh Cohort Study (HCS)

BackgroundCardiovascular diseases (CVDs) are the leading causes of global deaths. So, it is necessary to know the possible risk factors for each region. We aimed to assess the relationship between the risk of CVDs and sleep duration in the Iranian Arab population.MethodsIn this cross-sectional study, data from 8362 participants aged between 35 and 70 from the Hoveyzeh Cohort Study enrollment phase between 2016 and 2018 was analyzed. This study evaluated the association between ten-year CVD risk using the Framingham risk score and sleep duration. Self-reported sleep duration was categorized as short duration (equal to or less than 5 h), standard duration (6–8 h), or prolonged duration (equal to or greater than 9 h). Multivariable logistic regression to adjust for conventional CVD risks was used.ResultsAmong the assessed participants, 4892 (58.50%) were female, and the mean age was 47.93 (9.01). The average sleep duration was 7.59 (1.56) hours. The low, intermediate-to-high, and high CVD risk individuals were 6461 (77.27%), 1185 (14.17%), and 716 (8.56%), respectively. There was a significant relationship between prolonged sleep duration and lower odds of intermediate-to-high CVD risk in males (OR 0.66, 95% CI: 0.49–0.87, P-value: 0.004).ConclusionThe results of our study showed that longer sleep duration has a protective association with the intermediate to high risk of cardiovascular diseases in males. However, long and short sleep durations have no significant relationship with females’ risk of cardiovascular disease.

Organosilicon-Based Thin Film Formation in Very High-Frequency Plasma Under Atmospheric Pressure

Owing to recent interest in the production of flexible devices, it is necessary to develop a more convenient approach in which silicon (Si) thin film transistors (TFTs) are fabricated directly onto the flexible substrates at low substrate temperatures. Unfortunately, the physical limitations of conventional plasma-enhanced chemical vapor deposition (PECVD) under low pressures becomes a critical obstacle. In this study, Si film deposition using PECVD under atmospheric pressure excited by very high-frequency electrical power was investigated to overcome this issue. Tetramethylsilane [Si(CH3)4] is used as a source gas that is much safer than silane (SiH4) gas. We investigated the effects of the reactive gas concentration and specific energy (the ratio of input power to unit volume of the reaction gas) on carbon incorporation into the resultant films. Based on the results, we discuss the possibility of forming Si films with sufficiently low carbon content, which is applicable to Si TFTs.

Ultra-high growth rate of boron-doped diamond films with optimized growth parameters using in-liquid microwave plasma CVD

In this work, boron doped diamond (BDD) films were deposited onto a silicon substrate using the in-liquid microwave plasma chemical vapor deposition (IL-MPCVD) method. During the synthesis of BDD films, the effect of solvent, pressure, power and distance between the substrate and the microwave antenna on the growth rate of BDD films was studied. Pressure varied from 20 to 80 kPa at the interval of 20 kPa, power from 500 to 600 W at the interval of 50 W and distance from 1 to 1.5 mm. These different conditions resulted in the formation of both nanocrystalline and microcrystalline BDD films. Synthesized BDD films were characterized by Raman spectroscopy, laser microscopy, and optical emission spectroscopy. The highest growth rate of 410 μm/h is obtained as compared to the previous literature. Good synthesis parameters were used to deposit large area BDD films and the surface area expanded from 7 to 35 mm2. Along with this, the electrochemical properties of BDD films were studied in two different electrolytes. Concerning the growth rate, larger redox potential difference, IL-MPCVD is an effective method than the conventional microwave plasma chemical vapor deposition (MPCVD) method for the fabrication of high growth BDD films. Prime novelty statementIn this research, we synthesized BDD films with a B/C ratio of 1000 ppm by adjusting pressure, microwave power, and the substrate-to-electrode distance to determine the optimal synthesis conditions. This enabled us to determine the optimal synthesis conditions while examining variables like boron concentration and growth rate. By employing these optimized synthesis conditions, we successfully expanded the surface area of the BDD film from 7 to 35 mm2, which represents a fivefold increase. Most importantly, this is the first time reported the highest growth rate of 410 μm/h is achieved using this technique with to obtain highly crystalline BDD films. Additionally, we conducted an investigation into the electrochemical properties of BDD films in various electrolytes.

Nitrogen doping induced by intrinsic defects of recycled polyethylene terephthalate‐derived carbon nanotubes

AbstractThe indiscriminate utilization of nondegradable polyethylene terephthalate (PET)‐based products has triggered serious environmental pollution that has to be resolved vigorously. A simple synthesis of N‐doped carbon nanotubes from recycled PET (NCNTsr‐PET) was developed by a nitric acid‐assisted hydrothermal method. Experimental results and theoretical calculations show that the intrinsic defects in CNTsr‐PET would induce N‐doping by NH3 generated from nitric acid during the hydrothermal process, thus producing the NCNTsr‐PET. The life cycle assessment proves that the developed method for N‐doped CNTs using r‐PET as the carbon source is more environmentally friendly than the conventional chemical vapor deposition using acetylene as the carbon source. As a typical application, the NCNTsr‐PET delivered an impressive sodium storage capacity with an ultralong lifespan. This work not only provides a new route to upcycling waste plastics into valuable carbonaceous materials in an ecofriendly manner, but also reveals a basic understanding of the N‐doping mechanism in carbonaceous materials.

Epitaxial Growth of Boron Carbide on 4H-SiC

In this work, the successful heteroepitaxial growth of boron carbide (BxC) on 4HSiC(0001) 4° off substrate using chemical vapor deposition (CVD) is reported. Towards this end, a two-step procedure was developed, involving the 4H-SiC substrate boridation under BCl3 precursor at 1200°C, followed by conventional CVD under BCl3 + C3H8 at 1600°C. Such a procedure allowed obtaining reproducibly monocrystalline (0001) oriented films of BxC with a step flow morphology at a growth rate of 1.9 μm/h. Without the boridation step, the layers are systematically polycrystalline. The study of the epitaxial growth mechanism shows that a monocrystalline BxC layer is formed after boridation but covered with a B-and Si-containing amorphous layer. Upon heating up to 1600°C, under pure H2 atmosphere, the amorphous layer was converted into epitaxial BxC and transient surface SiBx and Si crystallites. These crystallites disappear upon CVD growth.

Micrometer-size crystalline monolayer MoS2 domains obtained by sulfurization of molybdenum oxide ultrathin films

In this work, the formation of micrometer-size crystalline monolayer (1L) MoS2 flakes with triangular shape and a central multilayer core is obtained by the sulfurization at 800 °C of pre-deposited ultrathin MoOx films (1.2–1.8 nm) on c-sapphire substrates. The thickness uniformity, crystalline quality, doping and strain distribution in the MoS2 flakes as a function of the initial MoOx thickness was evaluated by micro-Raman (μR) mapping. The excellent crystalline quality of the triangular 1L-MoS2 flakes was confirmed by micro-photoluminescence (μPL) maps, showing a very intense peak at ∼1.85 eV, that decreases in the central part, as expected for multilayers MoS2. A biaxial strain of ∼0.38–0.4% was deduced from the μPL data, in perfect agreement with μR results. Our results show how the sulfurization of pre-deposited MoOx films on c-sapphire allows, under proper conditions, to obtain 1L-MoS2 flakes with quality comparable to the one typically reported by the conventional chemical vapour deposition, with important implications for device applications.

An ultrasensitive FET biosensor based on vertically aligned MoS2 nanolayers with abundant surface active sites

Molybdenum disulfide (MoS2) nanolayers are one of the most promising two-dimensional (2D) nanomaterials for constructing next-generation field-effect transistor (FET) biosensors. In this article, we report an ultrasensitive FET biosensor that integrates a novel format of 2D MoS2, vertically-aligned MoS2 nanolayers (VAMNs), as the channel material for label-free detection of the prostate-specific antigen (PSA). The developed VAMNs-based FET biosensor shows two distinctive advantages. First, the VAMNs can be facilely grown using the conventional chemical vapor deposition (CVD) method, permitting easy fabrication and potential mass device production. Second, the unique advantage of the VAMNs for biosensor development lies in its abundant surface-exposed active edge sites that possess a high binding affinity with thiol-based linkers, which overcomes the challenge of molecule functionalization on the conventional planar MoS2 nanolayers. The high binding affinity between 11-mercaptoundecanoic acid and the VAMNs was demonstrated through experimental surface characterization and theoretical calculations via density functional theory. The FET biosensor allows rapid (within 20 min) and ultrasensitive PSA detection in human serum with simple operations (limit of detection: 800 fg mL−1). This FET biosensor offers excellent features such as ultrahigh sensitivity, ease of fabrication, and short assay time, and thereby possesses significant potential for early-stage diagnosis of life-threatening diseases.

Monolayer WS2 Nanosheets Passivated with HfO2 for Enhanced Photodetectors

Two-dimensional transition metal dichalcogenides (TMDCs) are widely used in electronic and optoelectronic devices. However, the conventional chemical vapor deposition (CVD) method is difficult to synthesize large-area monolayer WS2 nanosheets stably, which limits the application of WS2 in the field of photoelectric detection. In this work, we propose an innovative NaCl-assisted CVD method that allows freely adjustable substrate positions for synthesizing monolayer WS2 nanosheets. The obtained maximum grain size of the monolayer WS2 nanosheets is up to 30 μm. Subsequently, we investigated the effect of the HfO2 passivation layer on the performance of the metal–semiconductor–metal (MSM) WS2-based photodetectors. The HfO2 passivation layer brought an overall improvement to the performance of the fabricated photodetectors, exhibiting a high responsivity of 1093.1 AW–1, a high specific detectivity of 2.6 × 1012 Jones, and a high external quantum efficiency of 2.1 × 105%. Furthermore, the physical mechanism of the fabricated photodetectors has been discussed to explain how the HfO2 passivation layer takes effect in the improvement of the WS2-based photodetectors. This result can accelerate the development of optoelectronic devices based on TMDCs.

Wafer-Scale Patterning Synthesis of Two-Dimensional WSe2 Layers by Direct Selenization for Highly Sensitive van der Waals Heterojunction Broadband Photodetectors.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit promising potential in fabricating highly sensitive photodetectors due to their unique electrical and optoelectrical characteristics. However, micron-sized 2D materials produced by conventional chemical vapor deposition (CVD) and mechanical exfoliation methods fail to satisfy the demands for applications in integrated optoelectronics and systems given their poor controllability and repeatability. Here, we propose a simple selenization approach to grow wafer-scale (2 in.) 2D p-WSe2 layers with high uniformity and customized patterns. Furthermore, a self-driven broadband photodetector with a p-WSe2/n-Si van der Waals heterojunction has been in situ fabricated with a satisfactory responsivity of 689.8 mA/W and a large specific detectivity of 1.59 × 1013 Jones covering from ultraviolet to short-wave infrared. In addition, a remarkable nanosecond response speed has been recorded under 0.5% duty cycle of the input light. The proposed selenization approach on the growth of 2D WSe2 layers demonstrates an effective route to fabricate highly sensitive broadband photodetectors used for integrated optoelectronic systems.